1. Field of the Invention
The present invention relates to a combustion-engined tool including two opposite combustion chamber walls, and an ignition device arranged between the two opposite combustion chamber walls for igniting a fuel gas mixture occupying space between the two walls, with one of the two walls having a plurality of openings spaced from the ignition device.
2. Description of the Prior Art
A setting tool for driving in of fastening elements can serve as an example of a tool described above. Such setting tool is disclosed in German Publication No. 199 50 351. The setting tool disclosed in this German Publication includes two, extending parallel to each other, combustion chamber walls and an ignition device arranged between the two walls for igniting a combustible fuel gas mixture filling the space between the two walls, such as air-fuel gas mixture, oxigen-fuel gas mixture, or any other suitable combustible gas mixture. A cage is provided between the two walls in which the ignition device is housed. The cage has a plurality of openings formed in the circumferential wall of the cage, and one of the combustion chamber wall has a plurality of openings spaced from the cage.
The combustion starts when the available fuel gas mixture is ignited with the ignition device, and a flame front, which exits the cage, begins to laminary expand over the volume of the combustion chamber with a certain velocity. The flame front pushes the unconsumed fuel gas mixture in front of it, with the gas mixture flowing through the openings formed in the one of the combusting chamber walls from the fore-chamber, which is defined by the two walls, into another chamber adjacent to the wall provided with the openings, which adjacent chamber is called a main chamber. The gas mixture penetrating into the main chamber causes there turbulence and pre-compression. When the flame front reaches the openings, the flame penetrates through the rather narrow openings in an accelerated manner in form of flame jets into the main chamber, causing their a further turbulence. The intermixed gas-air mixture in the main chamber is ignited over the entire surface of the flame jets. It bums with a high velocity which noticeably increases the effectiveness of the combustion, insuring that cooling-down losses remain small.
If the laminar flame front in the fore-chamber after ignition propagates with a relatively low speed, a comparatively long time passes between the ignition and beginning of combustion in the main chamber, which leads to high cooling-down losses. Because of slow combustion in the fore-chamber, on the other hand, the piston starts to move prematurely, before the pressure reaches its maximum and, therefore, means for retaining the piston in its initial position until the pressure reaches its maximum, need be provided. With slow combustion and conversion of the fuel gas mixture in the fore-chamber, the flame jets, which penetrate into the main chamber, do not generate in the main chamber, upon penetrating thereinto, a sufficient by high turbulence.
Accordingly, the object of the present invention is to provide a combustion-engined tool of the type described above in which a high velocity of the flame front in the fore-chamber in insured.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing, between the ignition device and the openings in the combustion chamber wall separating the fore-chamber from the main chamber, means for localized swirling of the laminary expanding flame front formed in the fore chamber upon ignition of the fuel gas mixture with the ignition device.
The swirling device forms an obstruction in the fore-chamber in the path of propagation of the flame front, circumfluenting the same. As a result of interaction of the flame front with the obstruction, portions of the flame front are reflected from the obstacle or are deviated thereby, forming new flame front portions which increase the conversion rate of the fuel gas mixture. As a result, a localized turbulent combustion of the fuel gas mixture takes place, which results in a more rapid combustion of the entire gas mixture in the fore-chamber, which increases the propagation velocity of the laminar flame front. As a result, the cooling-down losses remain small. The flame jets, which penetrate into the main chamber are now capable to generate a sufficient turbulence when entering the main chamber. Therefore, the maximum pressure in the main chamber is obtained more rapidly, and the piston retaining means is not any more necessary.
The device for localized swirling of the ignited fuel-gas mixture in the fore-chamber can be formed as a separate, self-containing element, or be formed as additional structural components provided between the two walls. The swirling device can be formed, at least partially of wire, in particular, of a fine wire, in order to form simple, localized swirls. The swirling device can be formed, e.g., as a spring surrounding the ignition device and supported, at its opposite ends, against the two walls, respectively. As a spring, a helical spring can be used the advantage of which consists in that, upon collapsion of the combustion chamber, it can be compressed to a most possible extent, facilitating collapsing of the combustion chamber. Preferably, the spring is formed as a compression spring supported against the combustion chamber walls. In the compression spring, the distance between separate windings of the spring remains substantially the same which provides for a uniform distribution of the obstruction over the fore-chamber volume, which is circumfluented by the laminar flame front. This leads to a uniform conversion, as a result of the equipartition, of the fuel gas mixture.
Instead of a spring, the swirling device can be formed as a wire basket, which is formed of fine wire, with the bars extending perpendicular to the combustion chamber wall, and the like.
According to one of the embodiment of the invention, the device for swirling the flame front in the fore-chamber can be formed of structural elements associated with one or both combustion chamber walls. These structural elements can be formed as elements of facing each other surfaces of the two walls, e.g., as projections or recesses. The device-forming structural elements can be formed as steps provided in respective surfaces of the two walls. The surface elements of the two walls, which form the swirling device, can be arranged concentrically with the ignition device. Advantageously, the surface structural elements of the two wall are inversely arranged, so that the two wall can abut each other upon collapsing of the combustion chamber. In this case the projections on the surface of one of the wall would engage in the recesses formed in another of the walls, so that the walls can lie on each other.
The ignition device itself can be formed, e.g., of a pair of electrodes projecting into the fore-chamber. They are not necessarily need be surrounded by a cage. However, a cage can be used for housing the ignition device or the electrodes. When a cage is used, the swirling device is located outside of the cage, surrounding the cage and being spaced therefrom, a particularly high velocity of the flame front or the laminar flow is achieved.
It proved to be advantageous when the openings in the circumferential wall of the cage are angularity equidistantly spaced. The angularly equidistant spacing of the cage openings provides for symmetrical expansion of the laminar flame front in the fore-chamber to a most possible extent, and provides for symmetrical swirls of the flame front. This results in an overall improvement of the efficiency of combustion.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.